<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <!--
    select: 下拉菜单
    option: 菜单项
     ● selected: 默认选中
  -->
  <select name="colors" id="color-select">
    <option value="">请选择</option>
    <option value="red" selected>红</option>
    <option value="green">绿</option>
    <option value="blue">蓝</option>
  </select>
</body>

</html>